I actually pronounce them more similarly. [name]Air[/name]-ee-uhl is like the aerial antenna on the roof (before cable and digital tv). I pronounce [name]Ariel[/name] like air-ee-[name]EL[/name], or even [name]Ah[/name]-ree-[name]EL[/name], and [name]Arielle[/name], I would likely interpret as [name]AIR[/name]-ee-[name]EL[/name], and put the stress on the beginning like I would with [name]Arianne[/name]. I have never met an [name]Arielle[/name]. I realize this makes no sense phonetically, and there’s only a slight difference, but it’s at the beginning. The longer name doesn’t seem like “the same name” to me, it seems more like an Ar-i-elle, where the shorter name is more like a -ri-el, with an incidental A at the beginning.